A rotary self-cleaning strainer is typically attached to one end of a conduit whose other end is attached to the suction side of the pump. When the pump is operated, water is drawn through the strainer's screen while the screen prevents certain debris, such as that just mentioned, from entering the pump where it might otherwise possibly impair or even damage the pump. It is a typical practice to rotatably mount the screen on the body of the strainer and to situate interiorly of the screen a number of nozzles that are supplied with pressurized water, such as from a separate return line tapped into the pump's pressure side. These nozzles are aimed to direct water outwardly through the screen for the purpose of dislodging debris that has adhered to the screen's exterior due to the suction force of the pump acting through the strainer. The reaction of the screen to the force of the impinging water from the nozzles may be self-sufficient to rotate the screen without the use of an additional device such as a turbine. An example of a strainer having such nozzles effective to both rotate and clean the screen is illustrated in the commonly assigned U.S. Pat. No. 4,822,486, one of whose joint inventors is the present inventor.
While both the strainer of U.S. Pat. No. 4,822,486 and that of the present invention possess a cylindrical screen that is both rotated and cleaned by the impinging water from nozzles situated interiorly of the screen, the strainer of this invention differs from the patented one in that this new strainer is particularly suited for use with relatively small pumps, whereas that of the patent is intended principally for larger commercial applications. One of the motivations for the present invention is the recognition that there are many applications, typically private and non-commercial, where smaller pumps can be used to draw water from a natural body of water, yet previous rotary self-cleaning strainers would be too large and/or costly for such use or even incapable of being operated with the available pressurized water that can be returned to them. For example, an individual who owns waterfront property may be permitted to pump water from the adjacent body for watering a lawn or garden. A small pump that can suck water out of that adjacent body would be ideally suited for that purpose, but because the water contains debris like that mentioned earlier, such a pump cannot be reliable unless a means is provided to assure that such debris will not inhibit the effectiveness of the pump. The present invention is directed to a strainer that is ideally suited for such a purpose in a very cost-effective manner.
Briefly the present invention comprises a cylindrical screen that is disposed on a spool-like body structure for rotation thereon substantially about its own axis. Nozzles are disposed on the spool-like body structure interiorly of the screen and are connected to a source of pressurized liquid, typically pressurized water, which can for example be obtained from a tap at the pressure side of the pump. The nozzles are aimed toward the screen both to rotate the screen and to dislodge accumulated debris from the screen's exterior as the screen rotates. The spool-like body structure comprises a pair of discs that close the opposite axial ends of the screen. Each disc has an annular margin that coacts with the annular margin of the corresponding axial end of the screen, and the coactions of the discs with the screen are such that the screen is guided for rotation substantially about its own axis with a slight amount of axial and radial play that avoids binding of the screen between the two discs while maintaining sufficient disc/screen sealing to guard against unacceptable intrusion of debris between the coacting margins of the discs and screen. In this way, the use of separate devices, such as rollers or wheels, for guidance of the rotating screen on the strainer body is unnecessary, thereby saving on the size of the strainer and on the amount of labor and materials required to fabricate such a strainer. Moreover, the screen itself can be simply a length of perforated plastic strip of suitable width and thickness that is curled into a circular shape. Accordingly, a strainer embodying the inventive principles can be fabricated in an economical fashion thereby making such a device especially attractive to the consumer market, although it should be understood that commercial uses of the present invention are not precluded.
An attribute that is important in securing an acceptable construction for many uses of the invention involves a particular characteristic of the filter screen itself. This characteristic is the specific gravity of the filter screen. It has been found especially beneficial to make the filter screen of a material whose specific gravity is approximately that of water; in other words, the material of the filter screen is approximately neutrally buoyant in water. Such a physical characteristic is believed to enhance the performance of the strainer because it tends to make the screen somewhat self-centering between the closure discs when immersed in water and rotated. Such a tendency appears beneficial in minimizing screen/disc resistance as the screen rotates while protecting against unacceptable intrusion of debris at the interfaces between the margins of the screen and the discs.
As will be seen from the ensuing detailed description of a presently preferred embodiment of the invention, there are additional features, advantages, and benefits of the invention. Drawings accompany this disclosure and illustrate the best mode contemplated at the present time for carrying out the invention.